Clinical Study On Retraction Of Maxillary Anterior Teeth Using Microscrew Implants Combined With Long Retraction Hooks In Sliding Mechanics

Objective: This study aims to analysis the movement of the maxillary anterior teeth using long traction hooks in sliding mechanics combined with microscrew implants by comparing with short traction hooks and provide theoretical basis for en-mass retraction of the anterior teeth.Methods: 22 adult patients with maxillary protrusion and extracted bilateral maxillary first premolars were randomly divided into two groups,experimental group and control group and 11 patients in each group,who were treated with straight wire appliance and using microscrew implants anchorage.8 mm hooks in experiment group and 2 mm hooks in control group were used for the maxillary anterior teeth retraction by sliding mechanics.Cephalometric radiographs and maxillary dental cast were collected before and after the anterior teeth retraction,12 items of hard tissue measurements,6 items of soft tissue measurements and 4 items of dental cast measurements were measured.Mann-Whitney U test and Wilcoxon rank test were used for statistical analysis.Results: Hard tissue measurements showed the A points were retracted after the extraction space closed in both groups,and there was no significant difference between the two groups.The maxillary anterior teeth in the experimental group was less lingual inclinated than that in the control group and the difference was significant(P < 0.05).While the crown and root of maxillary anterior teeth were intruded more in the experimental group than that of the control group(P <0.05).Soft tissue measurements showed upper lip were retracted,extended and NLA increased after the extraction space closed in both groups and the differencce was significant(P < 0.05),but there was no significant difference between the two groups.The dental cast measurements showed that the maxillary anterior teeth in the control group has a larger reduction of the dental arch length than that of the experimental group(P < 0.05).The width of canine decreased after the extraction space closed in experimental group(P < 0.05).In the experimental group,the time needed for the closure of extraction space was longer than that in the control group and the difference was significant.Conclusions : With the retraction of maxillary anterior teeth,the alveolar bone was rebuilt and the A point were retracted.Upper lip were retracted,extended and NLA increased after the extraction space closed.The maxillary anterior teeth would be lingual inclinated when were treated with straight wire appliance and using microscrew implants anchorage combined with 8 mm or 2mm hooks for retraction.However,the 8mm hooks is superior to the 2mm hooks for the torque control and the intrusion of the maxillary anterior teeth,but the time used for closure is longer in the group of 8mm hooks.